I know just the place! One or two of the teeth seem to be bent, and the chain bumps against them in the small gear as it comes off the derailleur. The bike is an oldie but a goodie, an old MB-5 Bridgestone in dayglo grass green. Interesting bike. It's a MTB, but has road bike geometry, with the back tire tucked in close to the seat tube. It's like riding a road bike with fat tires and a flat bar. Below it is a Trek 830 I found this morning. MUCH longer back end.,,,,BD

This is a before pic, it's a lot cleaner looking now and has round profile tires